As illustrated in FIG. 14A and FIG. 14B, a bearing device for a wheel includes a hub wheel 2, an inner ring 3, an outer ring 4, and a plurality of rolling elements 5. A flange 6 configured to support a wheel is formed on an outer end portion of an outer peripheral surface of the hub wheel 2. Further, a first inner ring raceway 7 is formed on a middle portion of a shaft section 11 of the hub wheel 2, and a step portion 8 having a small outer diameter dimension is formed at an inner end portion of the shaft section 11 of the hub wheel 2.
The inner ring 3 having a second inner ring raceway 9 formed on an outer peripheral surface thereof is externally fitted to the step portion 8. A caulking cylindrical portion 17 as illustrated in FIG. 14A protrudes at the inner end portion of the shaft section 11 of the hub wheel 2. A portion of the caulking cylindrical portion 17 protruding inwardly from an inner end surface 10 of the inner ring 3 is bent by a caulking jig to an outer side in a diameter direction. In this manner, a caulking portion 16 as illustrated in FIG. 14B is formed, thereby being capable of sandwiching the inner ring 3 between the caulking portion 16 and a stepped surface 12 of the step portion 8.
Further, a first outer ring raceway 13 and a second outer ring raceway 14 are formed on an inner peripheral surface of the above-mentioned outer ring 4 so as to be opposed to the first inner ring raceway 7 and the second inner ring raceway 9, respectively. The plurality of rolling elements 5 are provided between the first inner ring raceway 7 and the first outer ring raceway 13, and the plurality of rolling elements 5 are provided between the second inner ring raceway 9 and the second outer ring raceway 14.
Hitherto, there have been proposed various methods and devices such as a method of manufacturing a rolling bearing unit for supporting a wheel, which achieves less formation of a crack or the like in a caulking portion (Patent Literature 1), a bearing unit for supporting a wheel, which is capable of reducing an amount of increase in diameter of an inner ring accompanied with formation of a caulking portion (Patent Literature 2), and a method of caulking a rolling bearing unit for supporting a wheel, which is capable of preventing distortion of an inner ring and formation of a crack in the inner ring when caulking is performed (Patent Literature 3).
In the method and the device described in Patent Literature 1 and Patent Literature 2, increase in inner diameter (hoop stress) during caulking is reduced by devising a chamfered shape of a radially inner surface of the inner ring. Thus, the inner ring is prevented from fracturing after caulking is performed. That is, a shaft of a hub wheel is expanded during caulking, and the expansion involves increase in diameter of the inner ring. Accordingly, the radially inner surface on a large end surface side of the inner ring, which is to be increased in diameter to a large degree during caulking, is formed into a tapered shape or a stepped shape. With this configuration, the increase in diameter of the inner ring (hoop stress) is suppressed.
Further, in Patent Literature 3, there is described the manufacturing method in which the increase in diameter of the inner ring is suppressed by restraining an outer diameter of the inner ring by a jig during caulking.